Due to advantages in terms of environmental protection, cleanliness, and saving energy, electric vehicles have been widely used during recent years. However, a main bottleneck in development of electric vehicles lies in batteries. In order to meet the demands in application of electric vehicles, a vehicle battery is required to have high performance and high power density. In addition, stable, efficient and fast charging technology is of crucial importance. Depending on arrangements, electric vehicle chargers can be divided into on-board chargers and ground chargers. A ground charger may be a AC (Alternating Current) charger, which charges a power battery assembly of an electric vehicle in a AC charging mode. A ground charger may be a DC (Direct Current) charger as well, which charges a power battery assembly of an electric vehicle in a DC charging mode. More often, the ground charger is a DC charger, so the DC charger is taken as an example in the disclosure. Output voltages and currents of the ground chargers have a large regulation range, and can provide several hundred kilowatts of charging power, which can realize fast charging of electric vehicles.
A ground charger of an electric vehicle is generally a conductive high-power ground charger. A power converter of the ground charger comprises a single-phase or three-phase uncontrollable rectifying bridge and a DC/DC conversion circuit. The single-phase or three-phase uncontrollable rectifying bridge rectifies single-phase alternating current or three-phase alternating current into direct current, so as to obtain a DC bus voltage. The DC-DC conversion circuit converts the direct current into a power supply with controllable DC voltage and DC current for charging the battery. Since the DC-DC converter in post-stage is with a buck converter topology, the DC bus voltage is clamped at a high voltage level. The output voltages of the charger are various, but the power converter with two-stage structure cannot well serve in some ranges of the output voltages. For example, in the range of high output voltage, the control method of the two-stage structure is not flexible enough, and the power conversion efficiency of it is low.
Therefore, there is a demand for an improvement in the structure of a power converter in the charger used for an electric vehicle and a control method thereof.